[scheduler] Move the translations inside `useEventCalendar()` and `EventCalendarContext`

[flaviendelangle]

Right now, only <EventCalendar /> has a translations prop.
We can add support for it on the standalone views by moving it to useEventCalendar() and dropping the translation context.
See if we want to add it to store.state.translations or as a new root property on the EventCalendarContext

ON HOLD: Not sure we want to do it. We need to decide if the l10n is on the headless package